Dear Tom and Ray: Last summer, my family and I loaded up the '91 Taurus and went for a drive in the mountains. When we got to an altitude of 8,000 or 9,000 feet, we seemed to lose more and more power, and about the only way to maintain speed was to floor it until we got into passing gear. I assume the car was suffering the effects of oxygen deprivation. Is there a simple adjustment that I can make to the car when we drive over the mountains again next year?
Tom: Well, I suspect that the only adjustment you could make would be to go around the mountains instead of over them, Mark.
Ray: Your car has a Manifold Absolute Pressure (MAP) sensor, which automatically adjusts the fuel mixture to compensate for altitude changes -- and the relative lack of oxygen at higher altitudes.
Tom: The problem is that it can adjust only so far. Once you get up to 8,000 or 9,000 feet, the air is getting pretty thin. And my guess is that the car just doesn't have as much air as it would like at that altitude. And when there's not enough air, the engine-management system cuts back on the gas. And when there's less air and gas, you get what? Less power.
Ray: Keep in mind, this car was not exactly overpowered to begin with. Plus, you're also asking the engine to do its maximum amount of work under those circumstances. You have got the whole family in the car, and you're climbing a mountain. So if that's the only time you've noticed the problem, I suspect it's an "environmental" problem rather than a mechanical one.
Tom: Of course, it's also possible that you have a clogged filter. If your fuel filter or air filter is clogged, for example, the car would demonstrate the same symptoms under maximum load. So have that checked. But my guess is you're just going to have to slow down and smell the fir trees next year, Mark.
Replacing struts in pairs
Dear Tom and Ray: I've got a simple question. Why do struts have to be replaced in pairs? I have a '93 Cavalier that had new struts put on a year ago after getting hit while parked. The same thing happened this year, and the left front strut was bent. My mechanic said he could only replace the struts in pairs, even though the right one wasn't damaged. I'm looking for an answer before I present the bill to the person who hit me, in case he questions it.
Ray: Well, Denise, there's no technical reason why you have to replace them two at a time. The problem is, the mechanic may only be able to buy them two at a time.
Tom: I don't know about all companies, but Monroe, for instance, sells most of its struts and shocks in pairs only now. So your mechanic may just be passing along this inconvenience to you.
Ray: In most cases, people are replacing struts because they're worn out, not because of an accident. And since they tend to be installed in pairs, they usually wear out about the same time. That's why they're usually replaced in pairs.
Tom: But I wouldn't worry about explaining that to the guy who hit you. I think he's more likely to question the new upholstery, the four new alloy wheels, and the new Bose sound system.
Write to Car Talk in care of The Buffalo News, P.O. Box 100, Buffalo, N.Y. 14240. Tom and Ray can't answer your letter personally but will run the best letters in the column. Their radio show airs at 6 and 10 a.m. Saturday and 5 p.m. Sunday on WBFO (88.7).